This application claims the priority of German patent application 100 49 911.2, filed 10 Oct. 2000 (PCT International Application No. PCT/EP01/11680, filed 9 Oct. 2001), the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method and apparatus for activating vehicle-occupant protection devices based on the approach speed of the vehicle relative to a collision object.
In methods for detecting impacts, acceleration signals from an acceleration sensor are usually evaluated and, as a function thereof, a decision is made as to whether a safety-critical hazardous situation is present and the airbag and/or other vehicle-occupant protection devices should be triggered.
For example, German patent document DE 197 29 960 discloses a method which measures an acceleration signal of an acceleration sensor to detect impacts, particularly in a motor vehicle for activating vehicle-occupant protection devices. The acceleration signal or a signal derived therefrom (for example the integrated acceleration signal), is compared, with a settable triggering threshold.
For this method, at least one sensor, referred to as a pre-crash sensor, registers the change in relative speed and/or the relative distance from collision objects within a proximity range of the vehicle surroundings. If the pre-crash sensor detects a safety-critical state, such as an imminent impact, the triggering threshold for activating vehicle-occupant protection devices is reduced.
Such a pre-crash sensor is preferably assigned to each side of the vehicle, and the triggering threshold of the side airbag located on the corresponding side is reduced (or not reduced) as a function of the signals determined by this sensor.
With this method, if a safety-critical state is detected within a proximity range of the pre-crash sensor by comparison with corresponding threshold values, the triggering threshold for activating vehicle-occupant protection devices is reduced. However, the triggering does not take place until after the acceleration signal or the signal derived therefrom has exceeded this corresponding triggering threshold.
Because this method reduces the triggering threshold only as a function of the relative speed and/or the relative distance from collision objects, influences such as, for example, the signal quality of a proximity sensor or the size of a collision object, cannot be taken into account in determining the level of the triggering threshold. For example, in the case of large collision objects it is not always possible to ensure that the sensor has also registered the smallest possible distance (closest proximity) between the sensor and vehicle. For this reason, in such a case the approaching collision object may impact with the vehicle somewhat earlier than was originally calculated.
German patent document DE 195 46 715 discloses a system for triggering a side airbag in which at least one sensor integrated in each door in the bodywork generates a control signal for the triggering electronics of the airbag. In this sensor system, at least two sensors are arranged spaced apart, one next to the other, and are integrated in the door in the bodywork. Each sensor has a transmitter stage and receiver stage which emits a microwave signal whose antenna lobe has a small half-value width and is perpendicular to the surface of the door. The microwave signals reflected at an approaching collision object are fed to an evaluation unit for generating an enable pulse.
However, with such an airbag sensor system it has been found that the sensor devices are already actuated directly by the pre-crash sensors, which drastically increases the risk of incorrect triggerings (for example, in the case of near misses). Such incorrect triggerings are especially disadvantageous because, under certain circumstances, the ability of the driver to react, particularly in the case of near misses, is very important; and his ability is greatly impeded by safety devices which trigger or have triggered.
A method and apparatus for controlling a triggerable vehicle-occupant restraint device is disclosed in European patent document EP 0 728 624 A3. In this method, the crash acceleration is determined and a crash value, which depends on the sensed crash acceleration, is determined. The latter value is compared with a threshold value, that is varied as a function of at least one target range, a target approach speed and an angle of incidence; and a triggering signal is provided if the crash value determined is greater than the threshold value.
However, such reduction of the triggering threshold for acceleration sensors in the case of an imminent impact has the disadvantage that it can lead to premature triggering of the vehicle-occupant restraint device if the acceleration triggering threshold is reduced to such an extent that it is already exceeded in the time period before the impact. This can take place, for example, if the vehicle travels over an unevenesses in the ground or a kerb stone just before the actual obstacle sensed by the proximity sensor.
An accident involving a side impact proves particularly critical in practice if the vehicle skids and moves in the transverse direction. Especially in the case of side impact sensors with radar or infrared, there may be repeated incorrect alarm triggerings when the vehicle travels closely past collision objects such as-parked vehicles or oncoming traffic. As a result, the triggering threshold of the acceleration sensors in the vehicle is reduced unnecessarily, increasing the risk of incorrect triggering of airbags, for example.
The radar sensor described in EP 0 728 624 A3 must also continuously calculate the approach speed of possible collision objects, the distance from such objects, the angle in respect of them etc., thus requiring a high degree of expenditure on processing signals, and a high level of computing power. Moreover, in order to reliably detect a side impact, at least two such sensors are required on each side, which gives rise to relatively high costs.
One object of the present invention is therefore to provide a method and apparatus for activating a vehicle-occupant protection device which uses simple components.
Another object of the invention is to provide triggering of a vehicle-occupant protection device in a way which is precisely adapted to the particular hazardous situation.
These and other objects and advantages are achieved by the method and apparatus according to the present invention, which uses simple sensors to generate what is referred to as a “time window”; i.e., a time range for a triggering request, in which the plausibility of a triggering request is confirmed after a threshold value is exceeded. Thereafter, if appropriate, activation of the vehicle-occupant protection device or devices takes place.
The method according to the invention achieves very exact and precise triggering or activation of the vehicle-occupant protection devices, taking into account the driving dynamics, geometry of the collision object and the signal quality of the respective proximity sensor which is used. For this purpose, the variables to be determined do not need to be measured continuously, for example over a certain range. Rather, it is sufficient for a single measurement to be started at a definable distance from an object.
With a device according to the invention, such a method can be carried out using simple proximity sensors. Because the approach speed to a collision object, the distance from it and the angle with respect to it do not need to be calculated continuously, there is also no need for a high degree of expenditure on signal processing. Thus large computing power is unnecessary, and the apparatus according to the invention can be implemented with simple and cost-effective components.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.